In the past, designers of light rail vehicles, and the authorities approving the safety of such vehicles, have concentrated on protecting the passengers on board the vehicle in the event of a collision. Less attention has been paid to the safety of pedestrians, cyclists, or passengers in automobiles or trucks that might be impacted by a light rail vehicle. Most light rail vehicles in service today have a non-retractable coupler at each end, which acts as an energy absorption device in the event of a collision between light rail vehicles, but as a battering ram in the event of a collision with an automobile or truck.
Some more recent designs of light rail vehicles use retractable couplers, which can be folded away when not in use. This removes the battering ram effect, but does nothing else to mitigate the consequences of a collision with vehicles and objects smaller than another light rail vehicle. Some authorities, mindful of the effective loss of energy absorbing capability when the coupler is folded away, have required energy-absorbing bumpers to be fitted onto the light rail vehicles. However, such bumpers have been specified as high energy-absorption devices designed for a collision between two light rail, vehicles. Such high energy devices would do little or nothing to help prevent injuries to pedestrians, cyclists, and automobile or truck passengers because of the high forces required to activate them. Some light rail vehicles use a plurality of impact energy absorption elements in conjunction with retractable couplers. In such systems, it is known to combine an energy absorption element with the mechanism holding the retractable coupler. It is also known to use a bumper to cover the retractable coupler while it is folded away, and when not in use. In such systems, the bumper and the energy absorption element in the retractable coupler mechanism provide a certain measure of safety for lower energy collisions. However, such systems have not been designed optimally to prevent injuries to pedestrians, cyclists, and automobile or truck passengers.
In complete contrast with the aims of prior art energy-absorbing systems, accident statistics show that the vast majority of collisions involving a light rail vehicle do not involve a second light rail vehicle. An automobile or truck was involved in 62% of cases reported to the Transit Cooperative Research Program, and pedestrians and cyclists were involved in 38% of all such cases. Slightly more pedestrians and cyclists than occupants of motor vehicles were killed. Collisions between two light rail vehicles are so rare that they do not even figure in the statistics. While rail to rail accidents do happen, such accidents tend to occur at relatively low speeds in the maintenance facility, when no passengers are on board.
In order to quantify the relationship between motor vehicle design and collision fatalities, the society of automotive engineers (“SAE”) has defined an “aggressivity index,” depicted in FIG. 1, which indicates the ratio of driver fatalities in collision partners to the number of crashes of subject vehicle. The SAE study shows that the most aggressive vehicles were full size vans with a rating of 2.47, followed by full-sized pickups with a rating of 2.31. Midsize cars had a rating of 0.70. The inventors of the present invention believe that the results of this study, and similar logic can be applied to understand collisions involving light rail vehicles. Based upon data from the Transit Cooperative Research Program, light rail vehicles have an aggressivity index of 21.0. In other words, light rail vehicles are 8.5 times more aggressive than the most aggressive motor vehicle in the SAE study.
Hence there is a need to equip light rail vehicles with an impact energy management system that will provide improved safety in all accident scenarios, from collisions involving a pedestrian to those involving a heavy vehicle, such as another light rail vehicle. Given such a wide range of different accident scenarios, the impact energy management system must be able to efficiently absorb a wide range of impact energies. Ultimately, such a system must be able to provide improved safety in all accident scenarios, especially the most likely ones involving pedestrians and cyclists.